The Digestive Tract

The digestive tract is a continuous tract throughout the body that interfaces with the environment at both its origin ,the oral cavities, as well as, at its termination, the anus. It is divided into different segments beginning with the oral cavity and followed by the pharynx, esophagus, stomach, small and large intestine, and the anus. There are also accessory digestive organs involved including the salivary glands, liver, pancreas, and gallbladder. Digestion begins in the oral cavity where the cheeks and lips press the food against the teeth, a process known as mastication. This is the first phase of mechanical digestion which is also aided by the tongue. There are three major pairs of salivary glands that secrete approximately 1 liter
Saliva contains a digestive enzyme called salivary amylase which breaks down covalent bonds between glucose molecules found in starches. Due to the brief time food is in the oral cavity only about 5% of carbohydrates are digested in the mouth. Saliva also protects the mouth from bacterial infection by producing lysozyme. The esophagus is a hollow, muscular tube that is approximately 25 cm long and has esophageal sphincters at the upper and lower ends which regulate movement of food and liquids through it. Peristaltic waves produced by contracting smooth muscle propel the food down the esophagus into the stomach cavity. The stomach has three parts, the superior portion is the fundus, the mid and largest portion is the body, and the small inferior portion is the pyloric. The stomach differs from other portions of the digestive tract in that it has three muscle layers used to produce a turbulent action necessary for digestion. There are multiple cell types in the stomach lining including the mucus, parietal, endocrine, and chief cells. The principle function of the stomach is to mix the food with digestive enzymes creating a semi-fluid mixture known as chyme. The digestive secretions in the stomach include hydrochloric acid, pepsin, intrinsic factor, and
Bile release by the gallbladder was triggered by hormonal and nerve stimuli and travels down the common bile duct where it joins the pancreatic duct before emptying into the duodenum. Bile in the duodenum helps to neutralize the hydrochloric acid as well as aid in fat digestion and absorption. Most of the bile is reabsorbed in the ilium and recycled for repeated